Evaluation system for obtaining diagnostic information from the signals and data of medical sensor systems

ABSTRACT

The invention provides a means of deriving highly reliable diagnostic information from the signals and data of medical measuring systems without first reducing the measuring data to individual characteristics and then associating these using decision trees in order to form a diagnostic conclusion. To this end, a comparator compares the measuring data recorded by a patient and provided by the sensor channels of a measuring system with measuring data which is stored in measuring databases and which is provided by comparable sensor channels of reference measuring systems. The data is compared in such a way that the reference measuring systems selected from the measuring databases are those which bear the most similarity to the measurements taken by the patient in terms of the measuring data of comparable sensor channels and which have a greatest possible number of the sensor channels which best match in terms of measuring data and which best correspond to each other. The selected reference measuring systems, along with the information belonging to the reference measuring systems of the measuring database and the comparison of this with the information belonging to the patient, are then used to form a diagnostic conclusion which applies to the patient with a certain degree of probability.

FIELD OF APPLICATION OF THE INVENTION

The invention relates generally to the field of medical diagnostics, andmore particularly to an evaluating system for obtaining diagnosticinformation from signals and data of medical sensor systems by means ofmeasurement data and patient databases.

CHARACTERISTICS OF KNOWN TECHNICAL SOLUTIONS

To an increasing extent in medical diagnosis use is made of systemswhich obtain diagnostic information from signals and data derived fromthe patient. This group of systems also includes the automaticallyevaluating electrocardiographs (EKG apparatus).

EKG evaluating systems, e.g. according to U.S. Pat. No. 5,022,404,detect one or more electrode potentials of electrodes attached to thepatient, and filter and digitalized them. Then these signals are fed viaa multiplexer to a microcomputer with CPU, work memory, etc. existing inthe EKG evaluating system. The computer processes the measured signals,e.g. by removal of the baseline drift according to DE 41 06 856, U.S.Pat. No. 5,357,969 or the removal of muscle artefacts from the EKGaccording to U.S. Pat. No. 5,259,387. Moreover, it calculates themedical derivations necessary for medical analysis of the EKG accordingto Wilson, Goldberg, Einthoven and/or the orthogonal derivationsaccording to Frank. At its simplest these medical derivations are eithershown on paper strips and/or electronic displays, e.g. in U.S. Pat. No.5,022,404 on LCDs, and evaluated by the doctor doing the evaluation.More intelligent, so-called evaluating electrocardiographs use themicrocomputer existing in the apparatus for, apart from signalprocessing and display, also signal evaluation, signal measurement and,if occasion arises, for the output of diagnostic information such ase.g. in U.S. Pat. No. 5,029,082.

Signal measurement and evaluation are effected, as described in patentsof which more details are given below, as a rule in such a way that fromthe calculated medical derivations are determined a number of individualsignal parameters important for cardiological assessment of the EKG withrespect to time and amplitude or criteria derived therefrom. A problemwith this determination of individual signal parameters is the differentapproaches, such as e.g. in exact determination of the zero line of theEKG for determining the starting point of the P wave and the resultingdetermination of the duration of the P wave, which deliver quitesubstantially differing results depending on the quality of the methodused. The patents are amongst others DE 43 10 412 (evaluation of the STsegment or other T wave), DE 39 27 709 (evaluation of the ST section),U.S. Pat. No. 5,159,932 (filtering of the EKG, QRS finding, averaging)or U.S. Pat. No. 5,020,540 (analysis of the frequency structure of theQRST complex, waveform template). Further relevant patents containdetermination of individual parameters of the EKG, or serve to detectlimited diagnostic information, e.g. in U.S. Pat. No. 4,930,075(evaluation of the ST segment for the detection of ischemias), U.S. Pat.No. 5,025,794 (method of bidirectional filtering for the detection ofretarded potentials), U.S. Pat. No. 5,355,891 (automatic signalaveraging by beat triggering for the detection of retarded potentials),U.S. Pat. No. 5,341,811 (HP filtering of at least two channels, weighadaptive filters for common-mode rejection, retarded potentialdetection) or DE43 04 269 (evaluation of the ST section for theassessment of acute ischemic damage).

The signal parameters determined are printed out on the paper strip orindicated directly together with the signal path of the EKG. For theoutput of diagnostic information, in a more or less complicated brancheddecision tree the individual signal parameters determined are linkedtogether into meaningful diagnostic information. This is done forexample by the many programs forming the basis of computer EKGapparatus. Such decision trees can have for example the following form:“If parameter 1 occurs in conjunction with parameter 3 and/or parameter4 and in medical derivation a at the same time condition 1 is operative,from this can be inferred the diagnostic information xyz”. In this wayfor every known diagnosis a decision tree can be built up on the basisof individual signal parameters determined from the EKG in itsderivations. This method is extremely elaborate on account of the largenumber of influencing variables and parameters and requires extensivecardiological knowledge or experience. Changes or improvements in themethods for determining individual parameters, control of empiricallydetermined threshold values or new medical knowledge require sometimeselaborate program alterations and function tests and are thereforeassociated with high costs or require new EKG apparatus with the revisedprograms. The patent U.S. Pat. No. 5,355,892 therefore describes an EKGsystem with portable storage media (floppy disk drive) for the storageof both EKG and patient information, e.g. for hospital informationsystems, as well as for reloading or updating algorithms for EKGevaluation.

A more recent group of EKG apparatus or methods try to obtain limiteddiagnostic information from the EKG signal by means of adaptive neuronalnetworks such as e.g. DE 43 07 545 (multi-channel measurement ofelectrical and/or magnetic field variables at least during part of theheart cycle, evaluations with an adaptive classifier (neuronal networkfor the classification and location of ischemias and/or infarctions) orU.S. Pat. No. 5,280,792 (arrhythmia classification by means of acombination of time analysis and sample comparison as well as neuronalnetworks). A problem with these methods is both the high learning effortin training the neuronal networks and the fact that neuronal networksare themselves at the stage of applied basic research. A full analysisof an EKG with the aim of deriving complex diagnostic informationrequires, on account of the complexity of an EKG, a very high number ofneurons or, associated with this, a very high computing capacity.

A further group of EKG apparatus or methods serves for the analysis anddiagnosis of rhythm disturbances, e.g. for cardiac pacemakers or directcontrol of defibrillators. These include e.g. patents DE 32 09 850(classification of rhythm disturbances, evaluation by comparison of thecomplete curve of the EKG with EKG curves of the patient underexamination detected or calculated previously in a learning phase, fullstorage of an example of the EKG curve for each class of rhythmdisturbances of the patient under examination), U.S. Pat. No. 5,240,009(detection of rhythm disturbances by comparison of averaged and storedwaveform complexes with current complexes of the same patient), U.S.Pat. No. 5,217,012 (correlation of result-free portions of own EKG withareas of the EKG with rhythm disturbances, compression and storage ofthe result-free EKG areas, alarm criterion is exceeding the thresholdvalue of cross-correlation function) or DE 43 20 519 (measurement andcomparison of three heartbeat periods and then of at least fiftyheartbeat curves, diagnosis of heart rhythm disturbances). A commonfeature of all these methods is that in each case they test only certaindiagnostic groups or given individual features of the EKG.

AIM OF THE INVENTION

The invention makes it possible to derive diagnostic information withhigh reliability from recorded signals and data of electrical and/ormagnetic medical measurement systems, without reducing the measurementdata initially to more or less complex individual characteristics whichdepend on the progress of knowledge, and then linking these individualcharacteristics by means of decision tress or neural networks which aredifficult to modify, into diagnostic information.

It is the object of the invention to make the obtaining of diagnosticinformation from the measurement data of medical measurement systems,such as EKG systems, largely independent of the more or less complexevaluation of individual characteristics, which change constantly withthe progress of knowledge, and decision trees based on thosecharacteristics or the comprehensive process of training neuralnetworks. According to the invention the object is achieved by the factthat a comparator compares measurement data of a patient from one ormore sensor channels with all or some of the measurement data ofcomparable sensor channels of reference measurements stored in one ormore measurement databases and selects the reference measurements whichhave the greatest similarity to the patient's measurement with respectto the measurement data of comparable sensor channels and also a maximumpossible number of sensor channels which match most in the measurementdata and correspond to each other. A probability is also inferred from acomparison of the technical, medical, diagnostic and personalinformation belonging to the reference measurements of the measurementdatabase and the patients' diagnostic information.

PRACTICAL EXAMPLE

The invention will be described in more detail below by two practicalexamples. The associated drawings show:

FIG. 1: is a basic drawing of a local EKG recording system with adatabase on CD-ROM;

FIG. 1A: is a representation of a patient showing the location of somestandard electrodes;

FIG. 2: is a schematic drawing of the function of an example of thecomparator for deriving diagnostic information from the processedmeasurement data;

FIG. 3: is a representation of the result of an evaluation of an EKG inrelation to 370 EKG of a signal database (cardiac infarctions); and

FIG. 4: is a basic drawing of an EKG recording system with anetwork-based SQL database and network-based evaluation.

FIG. 1 illustrates a local EKG recording and evaluating system.Electrodes (E1-E3, etc.) attached to a patient (1) in the usual mannerare shown in FIG. 1A. A right leg electrode (not shown) is used as theground. In clinical practice, twelve leads are usually used in adiagnostic EKG, although there is no limitation to the number one mayselect for special purposes. Hence the showing of three electrodes(E1-E3) is illustrative. The electrical potentials of the patient'sheart are detected and amplified, filtered and digitized by ameasurement processing system (2). A microcomputer (3) calculatesmedical derivations from these processed measurement signals accordingto 12-channel standard derivations. The medical derivations are storedin their relationship as an EKG measurement and, if occasion arises,outputted via a printer (4) or displayed on a monitor (5). A database isstored on one or more CD-ROMs which are located in a CD-ROM system (6)connected to the microcomputer (3). The database contains EKGmeasurements recorded at an earlier time as well as further informationon these EKG measurements. The database may be stored on CD-ROMs orother suitable electronic mass storage means. The EKG signals of thereference measurements stored in the database also occur in the presentembodiment as 12-channel standard derivations. Here the bandwidth of thedigitized EKG signals contained in the database according to the Nyquisttheory corresponds to not more than half the scan rate of the EKGsignals recorded with the EKG recording and evaluating system. For eachpatient contained in the database, several EKG recordings can be storedat given time intervals in the present example. The other informationstored in the database includes patient-related information, informationon anamnesis, test results, laboratory values, medical diagnoses,information on the nature of the patient's treatment, drugsadministered, etc. A comparator (see FIG. 2) compares a patient's EKGmeasurement derivations with EKG derivations of reference measurementsstored in one or more measurement databases and selects the referencemeasurements which have the greatest similarity to the measurementrecorded by the patient with respect to the measurement data ofcomparable sensor channels and also a maximum possible number of sensorchannels which match in the measurement data and correspond to eachother. By comparing the medical, diagnostic and personal informationbelonging to the reference measurements of the measurement database,diagnostic information which applies to the patient can be inferred witha certain probability. The comparator can also be designed completely orpartially as a hardware circuit to save computing time. The basicprogress of evaluation is shown in more detail in FIG. 2. In the examplefor this purpose in a first step the individual medical derivations aVL,aVR, aVF, V1-V6, I, II, III of the 12-channel standard derivation arecompared with the comparable medical derivations stored in the databasewith respect to matching of their signal patterns. For example, thederivation V1 of the patient is compared with the derivations V1contained in the database, and a dimension figure K₁₁ to K_(1n) iscalculated for the degree of matching of derivation V1 with thederivations V1 _(n) of the n reference EKGs of the database. The same isrepeated for each medical derivation so that in the example for eachcompared EKG of the database there are twelve measurement figures K_(1n)to K_(12n) (taking 12 derivations into consideration) for the degree ofmatching of the respective comparable derivations.

These twelve measurement figures for each EKG are compiled into adimension figure R which describes matching of the recorded EKG witheach EKG stored in the database in its derivations.

The EKGs with the greatest matching in all their derivations, which showthe highest degree of matching of their signal patterns, are selected.The EKGs best matching the patient's measurements are selected fromthese EKGs with respect to further information contained in thedatabase. FIG. 3 illustrates one possible result of this selectionprocess for cardiac infarctions in a two-dimensional drawing showing thedegree of matching of the unknown patient EKG with the known data bankEKGs. The closer a database EKG is placed to the bottom right corner,the greater its matching with the FKG of the patient. More extensivedifferentiation of the selection in the case of several data bank EKGswhich match the patient EKG well, can be obtained by assigning thediagnostic information contained in the database to that of the patient.

An essential advantage of the solution according to the invention is thepossibility of improving the reliability of detection of EKG analysissystems by simply extending the number of EKGs and associated referenceinformation contained in the database, by reflecting the naturalbiological variability in a more representative fashion and soincreasing the probability of finding one or more EKGs in the databasesimilar to the patient's EKG.

FIG. 4 describes another possible embodiment. The electrical potentialsof a patient's heart field are measured, filtered and digitized by anEKG sensor system (11) having sensors at certain points of the uppertorso of the patient (12), the sensor system being connected to anetwork. A database (3) with measurement signals of comparable EKGmeasurements together with further information belonging to themeasurement signals, so-called reference measurements, are located on apowerful computer system (14) which is installed at a central locationand connected to a network. Both the EKG sensor system and the computersystem (14) containing the database are connected to each other by alocal or worldwide network (15) of sufficient transmission capacity.This network (15) can be formed by a LAN in a hospital or by telephonelines, ISDN dialing lines or the Internet.

The measurement data together with other particulars relating to thepatient (12) are transmitted by the EKG measurement processing system(11) in a first step via the network (15) to the computer system (14)with the connected database (13). The computer system (14), as alreadydescribed in more detail for example in FIG. 2, selects the EKGs of thedatabase (13) which have the maximum possible matching both in theirindividual medical derivations and in the entirety of their measurement,and for which there is maximum possible matching between patient anddatabase with respect to further particulars. Following evaluation bythe computer system (14), the results of the comparison are transmittedback via the network (15) to the EKG measurement processing system (11)and indicated at the location of the EKG sensor system or outputted insuitable form or fed directly to corresponding hospital informationsystems.

Advantages of this solution lie in the possibility of building up asubstantially more powerful computer system (14) at a central locationwith a substantially larger and more complex database than would bepossible in local EKG apparatus with conventional evaluation. This leadsto more precise information on the EKG to be evaluated, as it dependsonly on the quality of the database, i.e. the number of EKG measurementsstored and their matching with the possible biological diversity ofcardiological results. Furthermore with suitable efficiency both of thenetwork (15), the central computer (14) and the database (13), severalEKG sensor systems can be operated at the same time. Moreover, in thisway the costs of the EKG recording system can be reduced, because thelatter does not have to contain its own diagnostic evaluation or its owndatabase.

If such a system is installed for example in a cardiological hospitalwith very high EKG yields, then at a suitable moment, for example at theend of the patient's treatment, his EKG signals and other personalinformation can be added to the database, thereby enhancing thedatabase. This results in a knowledge base which represents biologicaldiversity better and better.

What is claimed is:
 1. An evaluating system for obtaining diagnosticinformation for a current patient from signals of medical systems,including: a medical sensor system having a plurality of sensor channelsfor detecting biological activities of a patient over a given period oftime and outputting corresponding sensor signals; at least one databasecontaining a plurality of reference data sets, each reference data setincluding comparable sensor signals and technical, medical, diagnosticand personal information for a past patient; a comparator incommunication with the medical sensor system and the database whichcompares the sensor signals with the comparable sensor channels of thereference data sets stored in the database, wherein the comparatorselects reference data sets having similar sensor signals to the sensorsignals of the current patient; and a computer which determines aprobability for the selected reference data sets by comparing thetechnical, medical, diagnostic and personal information of the selectedreference data sets with technical, medical, diagnostic and personalinformation from the current patient.
 2. An evaluating system forobtaining diagnostic information from signals of medical systemsaccording to claim 1, wherein the sensor channels provide a continuoussequence of sensor signals over a given period of time and one or moresegments of limited time from this continuous sequence of measuredvalues.
 3. An evaluating system for obtaining diagnostic informationfrom signals of medical systems according to claim 1, wherein eachreference data set in the database also contains additional personalinformation of the past patient which is used by the comparator tofurther adjust the probability of the reference data set.
 4. Anevaluating system for obtaining diagnostic information from signals ofmedical systems according to claim 1, wherein the database containsreference data sets having sensor signals and technical, medical,diagnostic and personal information from both healthy persons and sickpersons.
 5. An evaluating system for obtaining diagnostic informationfrom signals of medical systems according to claim 1, wherein newreference data sets are added to the database.
 6. An evaluating systemfor obtaining diagnostic information from signals of medical systemsaccording to claim 1, including an electronic storage medium on whichthe database is stored.
 7. An evaluating system for obtaining diagnosticinformation from signals of medical systems according to claim 1,wherein the medical sensor system further includes biological sensorsystems in communication with the sensor channels which are attached tothe patient.
 8. An evaluating system for obtaining diagnosticinformation from signals of medical systems according to claim 1,wherein the medical sensor system is an electrocardiograph recordingsystem.
 9. An evaluating system for obtaining diagnostic informationfrom signals of medical sensor systems according to claim 1, includingan electronic storage medium located remotely from the recording systemand on which the database is stored, and a data network by which thedatabase is available.
 10. An evaluating system for obtaining diagnosticinformation from signals and data of medical sensor systems according toclaim 1, wherein the medical sensor system is a cardiological recordingsystem.